Revert to using Newtonsoft.Json for parsing instance

[ivarne]

There was reported inconsistent behaviour when deserializing enums, which would likely be fixed if we add System.Text.Json annotations to Storage.Interfaces

The change was introduced in #853, so it makes sense to revert.
6bac8a1#diff-509e2ea0fedd1d6a1d2d1c84b39ad128f078c03b225ce39ef5b578614beccbadL1224-R1233

Related Issue(s)

• reported privately by @chrrust on slack

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[martinothamar]

Would like @HauklandJ to review here. Do we use string serialization of enums in our API? (as in IOptionsMonitor<JsonOptions>.Get(JsonSettingNames.AltinnApi)), or was it the other way around

[HauklandJ]

Would like @HauklandJ to review here. Do we use string serialization of enums in our API? (as in IOptionsMonitor<JsonOptions>.Get(JsonSettingNames.AltinnApi)), or was it the other way around

We use number serlialization of enums.

[ivarne]

We use number serlialization of enums.

That is not entirely correct, because in lots of places we use [JsonConverter(typeof(JsonStringEnumConverter))]. In this case this PR preserves the behaviour from v8.3.x and earlier, so I think this should be merged before releasing v8.5